Notes from RailsCasts Rack Middleware screencast

• Rack Middleware = filter which you can use to intercept a request and handle the behavior a little differently as it goes to and from the application
• Different between middleware & metal = Metal is an endpoint & middleware is designed to be more of a filter (changes behavior if it needs to.)
• Goes into /lib directory as a .rb file?
• All middleware takes a initialize(app) method. The app variable will hold the rails application
• Adding a call(env) method will make it override rails. This needs to return a array with the same 3 elements as a metal.
• to make rails use your middleware, add this to your environment.rb file inside the Initializer block: config.middleware.use “NameOfClass”
• ‘rake middleware’ will list out the middlewares used by your app
• You’ll need to restart the server every time you create/change  a middleware
• To execute your rails app from your middleware, just run .call on the rails app, ex: @app.call(env)
• you can assign parts of the response from a rails app to variables using something like this:
• status, headers, response = @app.call(env)
• and then you can call return those back to the real response using something like this:
• [status, headers, "Add stuff" + response.body]
• response.body assumes that the app is a rails app. this is not best practice.
• a better approach is to use [status, headers, self] together with def each(&block)

I just got done watching the screencast on Rails Metal by RailsCasts and I took some notes:

Rails Casts Notes: #150 Rails Metal

• Bypass rails routing
• Simple request that happens frequently.
• to generate: ruby script/generate metal name_of_metal
• stored under app/metal/
• in the generated code, the self.call(env) method should return an array.
  1. response code ex. 404 or 200
  2. hash of header options
  3. Body content
• Won’t be recorded in log file since it bypass that as well.
• When creating/changing a metal, you need to restart server
• If there is a conflict between Rails routing and metal, metal wins because it gets the request before rails has had a chance to process it.
• “ab -n 100 http://127.0.0.1:3000/processes/list” will run a benchmark that you can use to compare performance (just replace the url of page)